/*
 Licensed to the Apache Software Foundation (ASF) under one
 or more contributor license agreements.  See the NOTICE file
 distributed with this work for additional information
 regarding copyright ownership.  The ASF licenses this file
 to you under the Apache License, Version 2.0 (the
 "License"); you may not use this file except in compliance
 with the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

package org.apache.flink.connector.base.source.reader.splitreader;

import org.apache.flink.api.connector.source.SourceSplit;
import org.apache.flink.connector.base.source.reader.RecordsWithSplitIds;

import java.util.Queue;

/**
 * An interface used to read from splits. The implementation could either read from a single split or from
 * multiple splits.
 *
 * @param <E> the element type.
 * @param <SplitT> the split type.
 */
public interface SplitReader<E, SplitT extends SourceSplit> {

	/**
	 * Fetch elements into the blocking queue for the given splits. The fetch call could be blocking
	 * but it should get unblocked when {@link #wakeUp()} is invoked. In that case, the implementation
	 * may either decide to return without throwing an exception, or it can just throw an interrupted
	 * exception. In either case, this method should be reentrant, meaning that the next fetch call
	 * should just resume from where the last fetch call was waken up or interrupted.
	 *
	 * @return the Ids of the finished splits.
	 *
	 * @throws InterruptedException when interrupted
	 */
	RecordsWithSplitIds<E> fetch() throws InterruptedException;

	/**
	 * Handle the split changes. This call should be non-blocking.
	 *
	 * @param splitsChanges a queue with split changes that has not been handled by this SplitReader.
	 */
	void handleSplitsChanges(Queue<SplitsChange<SplitT>> splitsChanges);

	/**
	 * Wake up the split reader in case the fetcher thread is blocking in
	 * {@link #fetch()}.
	 */
	void wakeUp();
}
